BillionToOne CEO exercises options, sells 8,333 shares

The transactions were made under separate Rule 10b5-1 plans adopted by Oguzhan Atay and his spouse in June 2026.

Rhea-AI Filing Summary

BillionToOne, Inc. (BLLN) Chairman and CEO Oguzhan Atay exercised 8,333 options at $2.80 per share on September 28, 2026, acquiring 8,333 Class A common shares and selling them at $120.64 per share under a Rule 10b5-1 plan adopted June 5, 2026. His spouse separately sold 2,666 shares at $120.64 per share that day under a plan adopted June 7, 2026; the spouse's reported indirect holdings after the sale were 154,502 shares. Atay's reported option position following the exercise was 493,629 options.

Insider Trade Summary 10b5-1

Exercise and sale activity reported; no spread calculated

Exercise and Sale 4 txns

Insider Atay Oguzhan

Role Chairman and CEO

Sold 10,999 shs ($1.33M)

Approx. gross sale proceeds $1.33M

Approx. exercise cost $23K

Type	Security	Shares	Price	Value
Exercise	Stock Option (right to buy) F4	8,333	$2.80	$23K
Exercise	Class A Common Stock F1	8,333	$2.80	$23K
Sale	Class A Common Stock F1	8,333	$120.64	$1.01M
Sale	Class A Common Stock F2, F3	2,666	$120.64	$322K

Holdings After Transaction: Stock Option (right to buy) — 493,629 contracts (Direct); Class A Common Stock — 0 shares (Direct); Class A Common Stock — 154,502 shares (Indirect, By spouse)

Footnotes (4)

1. F1. The transactions reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on June 5, 2026.
2. F2. The transactions reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person's spouse on June 7, 2026.
3. F3. Represents shares held by the Reporting Person's spouse.
4. F4. The options are fully vested and exercisable.

Key Figures

Options exercised: 8,333 options Exercise price: $2.80 per share Shares sold by Atay: 8,333 shares +4 more

7 metrics

Options exercised 8,333 options September 28, 2026

Exercise price $2.80 per share Options exercised September 28, 2026

Shares sold by Atay 8,333 shares September 28, 2026

Sale price $120.64 per share Atay's and his spouse's sales on September 28, 2026

Shares sold by spouse 2,666 shares September 28, 2026

Spouse's shares following sale 154,502 shares Indirect holdings following the sale

Atay's reported options following exercise 493,629 options Following the September 28, 2026 exercise

Key Terms

Rule 10b5-1 trading plan, Stock Option (right to buy), fully vested and exercisable

3 terms

Rule 10b5-1 trading plan regulatory

"effected pursuant to a Rule 10b5-1 trading plan"

A Rule 10b5-1 trading plan is a pre-arranged schedule that allows company insiders to buy or sell stock at specific times, even if they have inside information. It helps prevent accusations of unfair trading by making these transactions look planned and transparent, rather than sneaky or illegal.

Stock Option (right to buy) financial

"Stock Option (right to buy)"

fully vested and exercisable financial

"The options are fully vested and exercisable."

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How many BLLN shares did Oguzhan Atay and his spouse sell?

Atay sold 8,333 Class A common shares at $120.64 per share on September 28, 2026, under a Rule 10b5-1 trading plan adopted June 5, 2026. His spouse separately sold 2,666 shares at $120.64 per share that day under a plan adopted June 7, 2026.

What option position did Oguzhan Atay report after the BLLN exercise?

Atay reported 493,629 stock options following the September 28, 2026 exercise. The 8,333 options exercised that day were fully vested and exercisable and had an exercise price of $2.80 per share.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 09/30/2026 - 08:33 PM Accepted by SEC EDGAR 09/30/2026 - 08:33 PM Learn about SEC filing dates

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

X

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Atay Oguzhan

(Last) (First) (Middle)

C/O BILLIONTOONE, INC.

1035 O'BRIEN DRIVE

(Street)

MENLO PARK CALIFORNIA 94025

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
BillionToOne, Inc. [ BLLN ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chairman and CEO

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
09/28/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Class A Common Stock	09/28/2026		M(1)		8,333	A	$2.8	8,333	D
Class A Common Stock	09/28/2026		S(1)		8,333	D	$120.64	0	D
Class A Common Stock	09/28/2026		S(2)		2,666	D	$120.64	154,502	I	By spouse(3)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Stock Option (right to buy)	$2.8	09/28/2026		M			8,333	(4)	06/07/2031	Class A Common Stock	8,333	$2.8	493,629	D

Explanation of Responses:

1. The transactions reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on June 5, 2026.

2. The transactions reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person's spouse on June 7, 2026.

3. Represents shares held by the Reporting Person's spouse.

4. The options are fully vested and exercisable.

Remarks:

	/s/ Thomas P. Lynch, Attorney-in-Fact	09/30/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)